Minimizing waste disposal during surface cleansing for hot-dip metal coating

ABSTRACT

Cold-reduced flat-rolled low carbon steel strip is surface cleansed of ferromagnetic contaminants including iron fines, iron oxide particulate and associated debris which result from gauge-reduction operations. Such ferromagnetic contaminants are permanently removed from the strip steel hot-dip galvanizing system by dynamically concentrating such contaminant which are flushed to a magnetically-assisted particle separation container, formed from paramagnetic sheet material, which retains such contaminants, while cleansing solution at a desired purity level, is returned to the surface cleansing system; with sedimentation tank means providing for diminishing waste disposal concerns by separating sludge and recycling liquid.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-owned andcopending U.S. patent application Ser. No. 09/121,109, filed Jan. 23,1998, which was a continuation-in-part of copending and co-ownedapplication Ser. No. 08/794,783, filed Feb. 3, 1997, entitled CONTINUOUSPARTICLE SEPARATION OPERATIONS (now U.S. Pat. No. 5,830,282) which was acontinuation-in-part of copending and co-owned application Ser. No.08/445,530, filed May 23, 1995, entitled APPARATUS FOR CONTINUOUSFLAT-ROLLED STEEL STRIP CLEANSING AND FINISHING OPERATIONS (now U.S.Pat. No. 5,599,395).

INTRODUCTION

[0002] This invention relates to finishing operations involving hot-dipzinc spelter coating strip steel. In its more specific aspects thisinvention is concerned with minimizing aqueous requirements for causticcleansing solution supply purposes; and, with substantially-eliminatingaqueous waste discharge from surface-cleansing operations.

OBJECTS OF THE INVENTION

[0003] An important object is to provide for continuing uniform surfacecleansing by maintaining uniform purity-level standards for thecleansing solution.

[0004] Another object is to enable minimizing of waste disposal, inparticular, substantially-eliminating contaminated waste water disposal.

BRIEF DESCRIPTION OF THE DRAWING

[0005]FIG. 1 is a schematic general arrangement view for describingmethod and apparatus combinations of the invention;

[0006]FIG. 2 is a more detailed view of the circulating system forsurface cleansing solution of the invention;

[0007]FIG. 3 is a more detailed view of a magnetically-assisted particleseparator embodiment of the invention;

[0008]FIG. 4 is side-elevational view of the sludge-separatorsedimentation tank of the invention, and

[0009]FIG. 5 is an end elevated view of the tank of FIG. 4.

DETAILED DESCRIPTION

[0010] Contaminants, to be separated caustic surface cleansing solutionduring preparation of flat-rolled steel for finishing operations,comprise iron fines, particulate-iron oxide and associated debris.Priority levels for the cleansing solution are measured in parts permillions (ppm) of iron fines.

[0011] In continuous strip finishing mills, large surface areas of stripare handled per unit time; and, the solid contaminant quantities of ironfines from thickness gauge cold reduction operations, iron-oxide largelyresulting from hot rolling operations, and associated debris-resultingfrom the use of cold rolling oil, have in the past, required dumpinglarge-capacities of contaminated surface cleansing solutions.Contaminated cleansing solution, from large capacity facilities haverequired periodic dumping of large amounts of contaminated solution;which must then be fully replenished so as to involve an interruption inoperations. Dependent on production deadlines there can be a tendency toallow “purity levels” to rise significantly above a desired level.

[0012] Also, any requirement to dump those large contaminatedquantities, as taught herein, results in non-uniform surface cleansingduring line operation; which adversely effects the hot dip coatingoperations, the hot-dip coating apparatus, and is also detrimental tocontinuously annealing equipment located in-line between the surfacecleansing-operation and the hot dip coating apparatus.

[0013] The present invention provide uniform surface cleansing solutionand solves waste disposal problems now being experienced by mills incertain localities.

[0014] In the embodiment of FIG. 1, leading and trailing edges of coldrolled strip, from coils 10 and 12, are trimmed and directed, forjoining of such trimmed edges, into strip welder 14, so as to maintaincontinuous strip 15 during hot dip zinc-spelter coating finishingoperations.

[0015] For surface cleansing, continuous strip 15 is directed into acleansing tank means 16 having a large capacity for surface cleansingsolution.

[0016] Surface brushing stations 18 and 19 can augment the action of thecaustic cleansing solution 20, in the cleansing tank means 16.

[0017] Strip 22 travels from cleansing tank 16 into continuous annealingfurnace 24, for heating to a temperature of about 1000° F. in anon-oxidizing, preferably mildly-reducing, atmosphere to prevent surfaceoxidation; that atmosphere continues for subsequent introduction of thestrip, at about 900° F., into a hot-dip zinc-spelter coating bath (notshown).

[0018] Combinations of apparatus for maintaining desired purity levelsurface-cleansing solution are shown, and the combinations of steps aredescribed, in relation to FIG. 1.

[0019] During the surface cleansing operation, solution 20 iscontinuously, and controllable, withdrawn from holding means 16, anddirected, for example, by conduit 25 of FIG. 1 into a dynamic actioncontinuous filter, such as cyclone 26. The centrifugal force of cycloneapparatus 26 directs contaminants toward the side walls for accumulationand continuous-flushing removal at outlet 27, through conduit 28.

[0020] The filtrate, from which a significant percentages ofcontaminants are separated, is returned through conduit 29 to facilitycleansing tank means 16.

[0021] To assist compliance with restrictive sewer-disposal provisions,flushed contaminants are directed, in accordance with the invention,through conduit 28 to magnetically-assisted separator unit 30 (FIG. 1).A more detailed view, of the circulating system arrangement is shown inFIG. 2; and, also of the magnetically-assisted separator embodiment ofthe invention is shown in FIG. 3.

[0022] Referring to the schematic general-arrangement view of FIG. 1,magnetically-separated contaminants are retained in separator 30; and,the purified liquid portion of the material flushed disclosure fromcyclone 26 are returned, through conduit 32, to cleansing tank means 16.

[0023] Purity level, of the returning liquid is measured at the samplingstation shown by means gauge 34.

[0024] Contaminated solution from separator unit 30 can be releasedpromptly, including by washing the interior of that, unit. Drain valves35, 36, direct contaminated discharge from unit 30, through conduits 37,38 and 39, for sludge separation.

[0025] Capacities are selected such that the surface-cleansing operationneed not be interrupted for removal of contaminants.Magnetically-assisted particle separator 30 has a capacity equal toabout ten percent of the capacity of the surface-cleansing facility 16;and sludge-separating sedimentation tank 40 of FIG. 1 has about thirtypercent more capacity than that of separator unit 30.

[0026] Semi-solid sludge is transferred from sedimentation tank 40, byauger 42, into drum containers, such as 44 of FIG. 1. Such sludge can bedirected to a sintering plant for forming pellets for recycling in aniron-production unit and other recycling measures; or, can be directedfor solid waste-site disposal.

[0027] The solution in sedimentation tank 40 is decanted, from selectedheight-levels of tank 40; starting at the uppermost level, by use ofvalves 46, 47, 48 of each with associated conduits, as shown in FIG. 1.

[0028] Sludge is concentrated for removal by auger 42, with abouteighty-five to about ninety-five percent of the liquid received frommagnetically-assisted separator unit 30, being sufficiently free ofsludge for recycling through the magnetically assisted separator 30 andreturn to surface cleansing. Pump 50 (FIG. 1), by means of conduit 52and control valve 53, returns surface cleansing liquid, as shown, fromselected levels designated by valves 46, 47, and 48. Separator unit 30purifies decanted liquid for recycled use in the surface cleansingsystem.

[0029] Also, caustic, and fresh caustic cleansing solution, tocompensate for losses due to evaporation and/or product “drag-out”, areaugmented from source 54 (FIG. 1) through conduit 56. Valves 58, 59 arepositioned to direct solution from source 54 and to return from purifiedliquid from separator unit 30, and to return the filtrate from cyclone26 to selected locations of the surface cleansing facility, along theelongated holding means 16.

[0030] In FIG. 2, like reference numbers are used, where possible, indescribing the solution circulation system in more detail. Strip 15 isfed into the surface cleansing location, combines surface brushingcomponents in portion 60 and added cleansing solution in wash portion61. Surface-cleansed strip 22 is then directed for further in-lineprocessing. The combined cleansing solution capacity of solution 60, 61is about five thousand gallons.

[0031] Purity level of the surface cleansing liquid in ppm iron finescan be measured at gauge sampling locations 62, 63 and 64. One method isto remove contaminated solution at strip entry ends of elongated tankportions 60, 61; and, to return desired purity-level solution to thestrip exit area of portion 61, for counterflow, in relation to thestrip, in the surface cleansing system. Such counter-flow cansignificantly diminish particle quantities carried out, by the strip,into the annealing furnace.

[0032] Valves 65 and 66 (FIG. 2), at the entry and exit of particleseparator 30, enable isolation of that particle separator for drainageinto sedimented tank 40 (FIG. 1).

[0033] The magnetically asserted particle separator 30 (shown in FIG. 1and 2), utilizes paramagnetic polymer sheet material in forming theinterior and exterior walls of FIG. 3 polypropylene which can be bondedtogether to provide the desired capacity and direction of flow ofsolution being decontaminated. Permanent magnets are supported onpolymer coated plain carbon steel, or a paramagnetic stainless steel,frame so as to capable of being pivotally-rotated, as mounted on anexterior wall to terminate the magnetic flux action internally, forassisting in removal of contaminated contents.

[0034] As shown in FIG. 3, permanent magnets are mounted in rows 66, 67,68, 69 and 70 along the longitudinal end of separator unit 30 as shownin FIG. 3; and, can be mounted along side walls for higher separationcapacity than that of the specific embodiment being disclosed.

[0035] Pivotally-mounting the magnets externally, enables those magnetsto be readily moved into an orientation at an angle to the wall surface,such that lines of magnetic flux are no longer acting internally of unit30.

[0036] Permanent magnets can be housed internally between polymer sheetsat centrally-located wall petitions; such internal mounted magnet wouldnot be pivotally mounted; however, contaminants retained by such magnetscan be washed from adjacent polymer surfaces using pressurized watersupply available at mill sites. And, such pressurized water supply canbe used to augment removal from the internal wall surfaces of which haveexternally mounted magnets.

[0037] Floatation froth detainer 72 at the exit end of unit 30, preventsfloating debris from being pumped into the surface cleansing system. Thecapacity of unit 30 is about five hundred gallons; and, can be withdrawnsimultaneously at both longitudinal end valves 35, 36; or from a singlelongitudinal end portion of unit 30 by using a single valve separately.

[0038] Magnetically-assisted separator 30 can be drained and washed-downpromptly, at any time, without interrupting surface cleansingoperations. Typically, it would be drained when the return solution, atsampling gauge 32, shown in both FIGS. 1 and 2, exceeded a desiredpurity level, such as about fifty ppm iron fines. However, unit 30 canbe drained promptly at any time, and would ordinarily be drained, andcirculation continued, during regular periodic maintenance periods forthe processing line. Continuing the solution circulation system of FIG.2 at such time decreases the level of contaminant fines well below adesired operating maximum of about fifty ppm.

[0039] Contaminated cleansing solution drained, through valves 35, 36,of magnetically-assisted separation unit 30, is directed to inlet pipe76, got entering into a polypropylene sludge-separation sedimentationtank 40, shown in more detail in FIGS. 4 and 5. A polypropylene auger 42is located at the intersection of floor panels 78, 79 of sedimentationtank 40, such panels are angled downwardly for semi-solid sludge toauger 42 for removal.

[0040] Liquid decanting valve means 46, 47, 48 are each shown at itsrespective decanting level in FIGS. 4 and 5. Sedimentation tank 40 iscovered by cover plates shown at 80, 81, 82 in FIG. 4; a vent port 84 isprovided as shown in FIGS. 4 and 5.

[0041] The magnetically-assisted particle separator 30, sedimentationtank 40, and auger 42 preferably fabricated from an engineered polymer,such as polypropylene.

[0042] The cleansing caustic is available from Elf Autochem NorthAmerica, Inc., 2375 State Road, Cornwall Heights, Pa. 19020; andseparation equipment 26, for dynamic flow separation of solids andliquids, is available from Lakos Separators USA, 1911 North Helm Avenue,Fresno, Calif. 93727; interval or continuous flushing of purged materialis available on such units.

[0043] For purposes of measuring iron fines in ppm, five thousandgallons of cleansing solution are equal to slightly more than sixhundred thousand ounces of solution. The embodiment being disclosed canmaintain a uniform low level of less than about thirty ppm iron fines,by using six hundred gauss magnets, supplied by Eriez Magnetics, ofErie, Pa., under the heading of “Extra Power 600”. Added strengthmagnets extending to about fifteen hundred gauss are available.

[0044] Applicable data for continuous-strip zinc spelter cleansingoperations, for a continuous hot-dip coating line, are set forth below:TABLE I Surface Cleansing Solution about 5,000 gals Holding andScrubbing Tank 16 Withdrawal Rate of Dynamic about 2,700 gals/hr FilterApparatus 26 Rate of Filtrate Return from 26 about 2,300 gals/hrMagnetically-Asserting about 500 gals Separator 30, Capacity RateFlushed Purged From 26 about 400 gals/hr Magnet Field Strength 600 gaussper magnet Number of Magnets Per Row 4 Total Magnets on Entrance SideEndwall 12  Total Magnets on Exit Side Endwall 8 Capacity ofSludge-Separation about 650 gals. Sedimentation Tank 40

[0045] While specific materials, capacities, flow rates and other datahave been set forth for purposes of describing an embodiment of theinvention, it should be recognized that in the light of the aboveteachings, those specifics can be changed without departing from theprinciples of the invention; therefore is determining the scope ofpatentable subject matter, references should be made to the appendedclaims, as well as the above description.

1. Method for surface cleansing of flat-rolled continuous-strip steel inpreparation for in-line heat treatment and hot-dip metal coating,comprising A. providing for extended-length submerged travel ofcontinuous-strip steel, through a surface cleansing facility withsolution holding means for dislodging surface contaminants, consistingessentially of iron fines, iron oxide particulate and associated debris,while such strip is moving in the direction of its length at a desiredline speed commensurate with subsequent in-line processing requirements;B. selecting a purity level range for such surface cleansing solutionfor sustaining desired surface cleansing; C. continuously regeneratingsuch cleansing solution, during such continuous in-line operations, toestablish a purity level within a selected part-per-million range forsolid particulate, by: (i) controllably withdrawing cleansing solutionfrom such facility holding means at a predetermined rate, (ii) directingsuch withdrawn cleansing solution to dynamic means for physicallyseparating such contaminants, so as to obtain filtrate within suchselected purity-level range, (iii) returning such filtrate to suchholding means for continuing use in dislodging such surface contaminantsfrom such submerged continuous-strip; D. providing formagnetically-assisted contaminant separation within paramagnetic sheetmaterial container means; (i) defining such a contaminated-solutionseparator container means to have significantly less capacity than suchcleansing-facility holding means, (ii) presenting at least oneextended-area wall having an internal surface and an accessible externalsurface of such paramagnetic material, (iii) positioning permanentmagnet means for establishing lines of magnetic flux acting internallyof such contaminant-separator container, so as to attract and retainiron fines, iron oxide particulate and associated debris, by (iv)supporting such magnet means contiguous to such an accessible externalwall surface, opposite to such at least one internal wall surface; E.flushing such physically separation materials by selection liquidselected from the group consisting of (i) contaminated cleansingsolution, and (ii) an aqueous liquid compatible with such cleansingsolution, F. directing such flushed contaminants into such paramagneticsheet container means for attraction and retention of such contaminantsby such lines magnetic flux acting internally of such separatorstructure, while G. returning flushing liquid, which has been subjectedto such lines of magnetic flux, to obtain a desired parts-per-millionpurity level within such selected range for cleansing solution in suchin-line holding means; H. periodically discharging suchmagnetically-accumulated contaminants and flushing liquid from suchparamagnetic sheet container into sedimentation tank means forminimizing waste disposal concerns; by, I. providing for returningliquid from selected levels within such sedimentation tank means, to themagnetically assisted contaminant separation container, for recycled usein removing surface contaminants, and J. providing auger means disposedfor removing semi-solid contaminants from such sedimentation tank forselection from the group consisting of iron particulate utilization andsolid waste site disposal.
 2. The process of claim 1 , includingproviding for such submerged travel of surface-contaminated stripthrough a holding means having a capacity of about ten times thecapacity of such magnetically-assisted separator container means, andproviding a sedimentation tank capacity which exceeds such separatorcontainer means so as to provide for providing removal of the capacityof such separator container means for separation of solid contaminantsand retain such solution.
 3. The method of claim 2 , in which suchcleansing solution comprises a caustic alkali detergent cleansingsolution, further including (a) replacing such alkali cleansing solutionso as to make up losses due to evaporation and in-line operations striptravel losses, while (b) avoiding interruption of in-line processingoperation for removal or replacement of large quantities of suchcleansing solution, from such system.
 4. Apparatus for decontaminatingcaustic surface-cleansing solution, for iron-bearing product, duringmill processing prior to in-line heat treatment, comprising A. meanssupplying a surface-cleansing facility with solution for in-linecleansing of iron-bearing work product, including: (i) holding means forsuch surface-cleaning, solution with a capacity which is correlated withproduction capacity of such mill processing; (ii) selecting an ironcontent purity level range for such surface-cleaning solution duringmill processing; B. means directing for controlling withdrawal rate ofsuch cleansing solution from such surface-cleansing holding means; C.means for dynamically filtering iron fines, iron oxide particulate andassociate debris from such cleansing solution and returning filtrate tosuch holding means, D. means for flushing separated contaminant fromsuch dynamic filtering means and directing such withdrawn solution tocontainer means for magnetically separating iron fines, iron oxideparticulate, and associated debris with such container means beingformed from paramagnetic sheet material which is substantiallytransparent to lines of magnetic flux, E. permanent magnet means locatedfor establishing lines of magnetic flux acting internally of suchcontainer means for magnetically attracting and, at least temporarily,retaining such iron-fines, particulate iron oxide, and associated debriswithin such paramagnetic-material container means, F. means forreturning solution from which such solid contaminants have been removedand retained, to such holding means so as to maintain a purity levelwithin such selected range. G. means for periodically discharging suchsolid contaminants and contaminated solution from suchmagnetically-assisted separator means when such returning solutionexceeds such selective range; and H. means for directing suchcontaminants into a sedimentation tank means, for diminishing wastedisposal concerns including: (i) liquid decanting means for returningsolution, from selected levels of such sedimentation tank, to suchmagnetic separator container means, and (ii) auger means for removingsettled sludge contaminants.